Combustor systems

ABSTRACT

The disclosure shows two versions of providing a venturi around a fuel spray cone in a mixing chamber having an axial, vortical flow of pressurized air therethrough. This mixture is discharged into a combustion chamber. The venturi maintains desirable low smoke formation while spacing the flame front of the ignited mixture from the spray nozzle to reduce its temperature and thus prevent undesired carbon formation thereon.

United States Patent Ekstedt Aug. 19, 1975 1 COMBUSTOR SYSTEMS 3,430,4433/1969 Richardson 60/39.65 3,570,242 3/1971 Leonardi 431/183 [75] hvemo3 3 Eksted" Cmcmnau, 3,589.127 6/1971 Kenworthy 60/39.65

[73] Assignee: General Electric Company, Primary ExaminerDoug1as HartCincinnati, Ohio Attorney, Agent, or Firm-Lee H. Sachs; Derek P. 22Filed: Dec. 2, 1970 Lawrence The disclosure shows two versions ofproviding a ven- [52] U.S. Cl. 60/39.74 R; 431/183 i around a f l SprayCone in a mixing Chamber [5 Clhaving an axial vortical flow ofpressurized air there- Field of Search 60/3965 39-74; 431/183 through.This mixture is discharged into a combustion chamber. The venturimaintains desirable low smoke [56] References Clted formation whilespacing the flame front of the ignited UNITED STATES PATENTS mixturefrom the spray nozzle to reduce its tempera- 1,290,607 1/1919 Lovekin431/183 ture and thus Prevent undesired carbon formation 1,322,99911/1919 Bester 60/39.65 thereon- 2,398,654 4/1946 Lubbock... 60/39.65 3Cl 4 D 3,285,007 11/1966 Carlisle 60/39.74 R raw'ng gums III!III/III/lfl PATENTEUAUG-I ems 3, 899 884 SWEET 1 [1F 2 INVENTOR. EDWARDE. EKSTEDT nrromiEY- PATENTEU W75 3, 899 884 SZIET 2 UF 2 INVENTOR.EDWARD E. EKSTEDT ATTORNEY- COMBUSTOR SYSTEMS The invention hereindescribed was made in the course of or under a contract, or asubcontract thereunder, with the U.S. Department of the Air Force.

The present invention relates to improvements in combustor systems,particularly in the generation of a hot gas stream as in gas turbineengines.

Combustor systems, as employed in gas turbine engines, comprise a spraynozzle which injects fuel into a combustion zone. Once ignited, acontinuous flame front is maintained in the combustion chamber as fueland pressurized air flow therein and a high energy, hot gas stream isdischarged therefrom.

Recent emphasis had been placed on the problem of minimizing smokegenerated in the combustion process and discharged to the atmospherefrom gas turbine engines. One highly successful approach to this problemhas been to discharge the fuel into a conduit or mixing chamber whichopens into the combustion chamber. Pressurized air is introduced axiallyand swirled vorti cally about the discharge axis of the spray nozzle. Inso doing, the turbulent flow field created produces a highly dispersed,over-stoichiometric mixture of fuel and air in the conduit. This mixtureis discharged in a generally conical fashion into the combustion chamberwhere it is further dispersed by additional air entering other openingsin the combustion chamber. This addi tional air is sufficient to sustaincombustion and a flame front is produced in this mixing zone at themixing chamber discharge. Because of the high degree of dispersionobtained, over-rich fuel zones are essentially eliminated and smoke isminimized to the point of being virtually undetectable.

While smoke is thus effectively reduced, the frequency of maintenance ofthe fuel nozzles has increased. This is due to the coking of fuel on thenozzles which adversley affects the pattern of the fuel spray conedischarged therefrom. Various forms of spray nozzles and air shroudstherefor have had limited degrees of success in overcoming this problemand still maintaining minimized smoke levels. This lack of success isattributed to the fine dispersion of fuel which recirculates, inlocalized regions, and contacts the discharge end of the nozzle. Thefuel then cokes or carbonizes when it contacts the nozzle due to thehigh temperature thereof.

Accordingly, the object of the invention is to reduce the temperaturelevels of fuel nozzles and, in so doing, minimize the buildup of carbonthereon and further, to maintain minimal smoke generation in thecombustion process.

These ends are broadly attained by providing a venturi means into whichthe fuel spray is discharged. The acceleration provided by the initialportion of the venturi tube accelerates mixing air introduced around thenozzle to an extent sufficient to prevent combustion for a predetermineddistance from the nozzle. By thus displacing the flame front from thenozzle, its temperature may be reduced sufficiently to preventundesirable carbon buildup thereon. The divergent portion of the venturitube re-expands the mixing air to discharge it into the combustionchamber at a relatively wide angle consistent with the smoke minimizingdispersion process referenced above.

Other features are found in the relationship of the venturi tube to themeans for introducing mixing air as well as in the amount of mixing airintroduced.

The above and other related objects and features of the invention willbe apparent from a reading of the following description of thedisclosure found in the accompanying drawings and the novelty thereofpointed out in the appended claims.

In the drawings:

FIG. 1 is a schematic representation of a gas turbine engine employing acombustor of the type herein referenced;

FIG. 2 is an enlarged longitudinal section illustrating the details ofthe combustor referenced in FIG. 1 as they embody the present invention;

FIG. 3 is a section taken on line IIl-IlI in FIG. 2; and

FIG. 4 is a longitudinal section, similar to FIG. 2, illustratinganother embodiment of the invention.

Referencing FIG. 1, the illustrated engine comprises an axial flowcompressor 10 which pressurizes air. This pressurized air flows throughan annular passageway 12 to an annular combustor 14 where fuel isintroduced. The pressurized air supports combustion of fuel within thecombustor to generate a high energy level, hot gas stream. This hot gasstream drives a turbine 16 which in turn powers the rotor of thecompressor 10. The hot gas stream is then converted to a useful outputas by being discharged from a nozzle 17 to provide propulsive. thrustfor an aircraft.

The combustor 14, as illustrated in FIG. 2, comprises outer and innerliners 18 and 20 which define an annular combustion chamber 21. Theseliners are joined by compositely formed dome portion 22 at theirupstream ends. Cylindrical conduits or mixing chambers 24 which openinto the dome portion 22 and the combustion chamber 21. Transitionsegments 26 blend the conduit openings into the dome portion. An axialflow swirler 28 is mounted at the upstream end of each conduit 24.

The swirler has a central opening which receives the discharge end 29 ofa fuel spray nozzle 30. The nozzle 30 may take many forms but ispreferably characterized by at least one orifice outlet which produces aconical spray discharge having a relatively large included anglerelative to an axis a which extends lengthwise of the mixing chamber.The swirler 28 includes a row of passageways 32 annularly surroundingthe axis of the nozzle discharge end 29. The passageways 32 are angledrelative to the nozzle axis to produce a vortical flow field.

The swirler 28 may be mounted on the upstream end of the conduit 24 inthe manner taught in copending US. application Ser. No. 796,391, filedFeb. 4, 1969 and of common assignment. The referenced application alsodescribes in further detail, the relationship of the swirler passageways32 in obtaining a high degree of fuel dispersion for low smokecombustion.

Introduction of pressurized air from the annular compressor dischargepassageway 12 into the combustion chamber 21 will now be described. Thepassageway 12 is defined by outer and inner, generally cylindricalcasings 34 and 36 which extend along the lengths of the liners 18 and 20are respectively spaced therefrom to define annular passageways 38 and40. An annular snout assembly 42 is secured to and projects upstreamfrom the liners l8 and 20. The snout assembly has a central passageway43 having an entrance facing the discharge passageway 12 and discharginginto an annular chamber 44 surrounding the entrances to the mixingchambers, i.e., swirler passageways 32. The pressurized discharge fromthe compressor then is split into three annular flow-paths alongpassageways 38, 40 and 43.

Air from the passageways 38 and 40 may enter the combustion chamber 21to serve three functions. First, it may pass through relatively smallholes 46 which are oriented to cool the liners 18 and 20. Second, it mayenter relatively large holes 48 to penetrate the combustion chamber andsupply requisite, primary air for the combustion process. Third, it mayenter holes (not shown) further downstream as dilution air to reduce thetemperature of the hot gas stream to a temperature compatible with thecapabilities of the materials forming the turbine. The air enteringholes 48 may also serve a dilution function.

Air entering the snout passageway 43 and chamber 44 is then metered byand injected into the mixing chamber as discrete jets by the swirlerpassageways 32. The vortical flow of mixing air is highly effective indispersing or mixing the fuel from the spray cone into fine dropletswhich support a combustion process at a flame front generally identifiedby the broken line in FIG. 2.

The flame front is primarily controlled by two factors, once ignition ishad. These are the presence and degree of a combustible mixture and thevelocity of that mixture. In accordance with the present invention,these factors are taken into account in maintaining a desired distancebetween the flame front and the discharge end 29 of the fuel nozzle tominimize the temperature of the latter.

To this end, a venturi tube 50 is disposed concentrically of the nozzleaxis a in a surrounding relationship with the spray cone discharged bythe nozzle. The inlet diameter of the venturi tube approximates the meandiameter of the annular row of swirler passageways 32. Thusapproximately one-third of the swirler mixing air is captured by andaxially accelerated through the convergent portion of the venturi tube50. This creates a condition of where the mixture, at the throat of theventuri, is sufficiently over-stoichiometric as not to supportcombustion and the mixture velocity is increased to further detercombustion. The divergent portion of the venturi tube then re-expandsthe mixture to approximately the original cone shape of the nozzledischarge. In this connection, it will be noted that the divergentportion of the venturi terminates at a generally tangent relationshipwith the spray cone.

While maintaining the desired low smoke characteristics, the venturitube 50 is highly effective in maintaining the flame front at a desireddownstream distance. This distance can be controlled as desired by thelength of venturi tube and its contraction ratio as well as the amountof mixing air flow therethrough, all of these factors being balanced sothat the spray cone angle is relatively divergent as it discharges fromthe venturi tube into the combustion chamber.

The effect of the venturi tube may be expressed in another fashion inthat it increases the total pressure in the core of the vortical flowfield created by the axial flow swirler. Without the venturi, the lowpressure of the vortical core would enable recirculating primary air toflow forwardly, as indicated by the broken arrows, and create acombustible mixture and flame front closely adjacent the nozzledischarge. With the venturi such recirculation occurs, as indicated bythe solid arrows, but is more limited in the magnitude of its upstreammovement.

It will be noted that the venturi tube is welded or otherwise bonded tothe swirler 28 intermediate the lengths of the passageways 32. In sodoing, added strength and rigidity is obtained for the swirler.

FIG. 4 illustrates an embodiment of the invention wherein all of themixing air flows through a venturi tube 52 which also serves as a mixingchamber for introducing the dispersed fuel mixture into the combustionzone. The action of this venturi in obtaining a desired downstreamdisplacement of the flame front and a consequent reduction in nozzletemperature is essentially the same as previously described except thatthe velocity factor of the venturi is more predominant in displacing theflame front since a greater amount of air enters the venturi. In fact,the benefits of the broader aspects of the present invention can beattained where the amount of mixing air flow is sufficient to produce acombustible mixture in the mixing chamber.

It has been demonstrated that the described use of a venturi is highlyefiective in preventing carbon buildup on fuel nozzles and, thus,assuring long maintenancefree operation. At the same time, low smokelevels continue to be maintained. 7

While the invention has been described with reference to an annularcombustion system, it is equally applicable to a cannular system.Further, in the broader aspects of the invention, the mixing air couldflow through the mixing chamber with little or no vortical component.These and other variations in the described embodiments will occur tothose skilled in the art within the spirit and scope of the presentinventive concepts which are to be derived solely from the appendedclaims.

Having thus described the invention, what is claimed as novel anddesired to be secured by Letters Patent of the United States is:

1. A combustor system comprising:

a combustion chamber,

a mixing chamber opening into the upstream end of the combustionchamber,

a spray nozzle for discharging fuel as an atomized cone into said mixingchamber, the axis of said spray cone extending lengthwise of said mixingchamber toward said combustion chamber,

means for introducing pressurized air into the upstream end of saidmixing chamber and producing an axial flow field for dispersing the fuelin fine droplets,

venturi means surrounding said spray cone and through which at least aportion of the axially flowing air passes, and wherein the airintroducing means additionally provide a vortical component to the airflow field,

the venturi means comprise a venturi tube mounted within said mixingchamber,

a cylindrical conduit and an axial swirler at the upstream end of theconduit define said mixing chamber,

said air introducing means includes an annular row of generally radiallyon'ented passageways angled through said swirler,

said axial swirler has a central opening through which the discharge endof the spray nozzle projects, and

the inlet end of the venturi tube has a diameter intermediate theminimum and maximum diameters of the annular row of swirler passagewaysand is bonded to said swirler.

6 2. A combustion chamber as in claim I wherein the chamber at a rateinsufficient to produce a comdivergent discharge end of the venturi tubeterminates bustibie mixture with the f l introduced by said generally asa tangent to the spray cone discharge from Spray noflle and the nozzle.

3. A combustor as in claim 2 wherein: a pressurized plenum is provided,in combination with the upstream face of said axial swirler, and Producea Combustible mixture thereinthe swirler passageways meter air into themixing means are provided for introducing further pressurized air intosaid combustion chamber sufficient to

1. A combustor system comprising: a combustion chamber, a mixing chamberopening into the upstream end of the combustion chamber, a spray nozzlefor discharging fuel as an atomized cone into said mixing chamber, theaxis of said spray cone extending lengthwise of said mixing chambertoward said combustion chamber, means for introducing pressurized airinto the upstream end of said mixing chamber and producing an axial flowfield for dispersing the fuel in fine droplets, venturi meanssurrounding said spray cone and through which at least a portion of theaxially flowing air passes, and wherein the air introducing meansadditionally provide a vortical component to the air flow field, theventuri means comprise a venturi tube mounted within said mixingchamber, a cylindrical conduit and an axial swirler at the upstream endof the conduit define said mixing chamber, said air introducing meansincludes an annular row of generally radially oriented passagewaysangled through said swirler, said axial swirler has a central openingthrough which the discharge end of the spray nozzle projects, and theinlet end of the venturi tube has a diameter intermediate the minimumand maximum diameters of the annular row of swirler passageways and isbonded to said swirler.
 2. A combustion chamber as in claim 1 whereinthe divergent discharge end of the venturi tube terminates generally asa tangent to the spray cone discharge from the nozzle.
 3. A combustor asin claim 2 wherein: a pressurized plenum is provided, in combinationwith the upstream face of said axial swirler, and the swirlerpassageways meter air into the mixing chamber at a rate insufficient toproduce a combustible mixture with the fuel introduced by said spraynozzle, and means are provided for introducing further pressurized airinto said combustion chamber sufficient to produce a combustible mixturetherein.